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Miscellaneous Exercise · Q12

Q.A donuts shop offers 20 kinds of donuts. The shop has at least a dozen donuts of each kind if person enters the shop he can select dozen donuts in

(i) 31C12^{31}C_{12} ways
(ii) 30C12^{30}C_{12} ways
(iii) 32C12^{32}C_{12} ways
(iv) 240 ways
Sikkim CbseNCERTSubjective· 1mImportance★★★★★est
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Selecting a dozen donuts from 20 kinds, with each kind stocked in unlimited (at-least-12) supply and only the kind (not order) mattering, is a combinations-with-repetition count.

Ways to select rr items from nn distinct types, with unlimited repetition allowed and order not mattering: n+r−1Cr^{n+r-1}C_r.

  1. Here n=20n=20 (kinds of donuts) and r=12r=12 (a dozen to be chosen). Since the shop has at least a dozen of each kind, no kind is ever exhausted, so repetition is effectively unlimited. …

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